Spoilers where are you👀 Okay how is she their sister tho!?

I just read this from other spoilers

Background about her~

It is said that some evil noble kidnapped her at birth and toss her away and ended up as a slave.
That evil noble did that cause of his hatred to the royal family.
Dunno which house it is~
And as I can see here the brothers knew they have a little sibling and have been searching for her.

Oh now it makes sense why she end up being a slave. Thank you sm for the spoiler